Sensor cards are used in measuring instruments or analysis systems in which a liquid or gas sample is subjected to a chemical analysis, it being possible to quantitatively determine different analytes in gaseous and liquid samples. Analysis systems of this type are increasingly being used in medical technology, process control and also foodstuffs and ecological analysis.
In this case, the analysis of parameters of body fluids in the context of point-of-care (POC) testing in the field of medical diagnosis constitutes a main area of use of these analysis systems. In the treatment of acutely and critically ill patients, it is important for the treating physicians to obtain precise information about the patients' physiological blood parameters, preferably in a rapid and simple manner. These blood parameters may include the blood gases (pO2, pCO2, pH), the electrolytes (Na, K, Ca, Cl), the conductivity of the blood and, derived therefrom, the hematocrit and the metabolites (glucose, lactate, urea, creatinine). In this case, the analysis location is increasingly being shifted away from the central laboratory personnel to those who also care for the patient. A considerable amount of time is thereby gained, which benefits a more rapid and more efficient treatment of the patient.
In developing the analysis systems used for this purpose, it is particularly important in this respect that the apparatuses can be operated simply and reliably and do not need complicated and time-consuming maintenance measures and the analysis costs per sample are kept as low as possible. There are currently known various conventional clinical analysis systems used for this objective. The conventional clinical analysis systems use predominantly electrochemical sensors for measuring the analytes. In this case, some systems use sensors of conventional design comprising electrode body, inner electrolyte and analyte-selective membrane, which last a long time but have to be maintained repeatedly in a time-consuming manner.
Recent analysis apparatuses are increasingly using maintenance-free planar sensors that can be mass-produced for instance by methods of thin-film and thick-film technology. A plurality of sensors, each of which can specifically determine an analyte, are applied on a substrate. In the flow cell, calibration solution and liquid samples are passed over the sensors in order to determine the analyte concentrations.
At the 17th International Symposium of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), June 1998 in Nice, France, a new generation of sensor cards was presented which utilize the so-called double matrix membrane (DMM) technology. The conventional sensor cards with double matrix membranes have a sensor film with openings that face the liquid sample to be examined in the use position. A covering film is arranged on that side of the film which is remote from the liquid sample. Electrical conductor tracks made of silver/silver chloride are printed on the said covering film. The conductor tracks face the sensor film. Arranged between the sensor film and the covering film are carrier materials for ion-selective DMM sensors, which adjoin an opening in the sensor film and one of the films. The sensors are connected such that the openings in the sensor film are smaller than the sensor area, so that the edge of the opening presses down the edge of the sensor, which ultimately leads to a raising of the edge of the opening. The electrical tapping is effected directly at the conductor tracks, which, for this purpose, extend as far as the edge of the covering film, which is made larger than the sensor film, so that a part of the conductor track is not concealed by the sensor film and can be tapped.
Within the analysis system, the conventional DMM sensor card is connected in sheet-like fashion to a plate in which one or a plurality of grooves are situated. This connection gives rise to a flow channel for the liquid sample which is bounded by the wall of the grooves, on the one hand, and by the sensor film of the DMM sensor card, on the other hand. In this case, the openings in the sensor film point towards the flow channel, so that the sensors can be wetted with the liquid sample flowing through the flow channel. The conventional DMM sensor card has the disadvantage that it does not ensure reliable sealing of the flow channels within the plate.
Thus, there is a need for a sensor card for determining analytes in liquid samples which ensures a reliable sealing of the flow channels for the liquid sample, and also of specifying a method for producing such a sensor card.